The 01M transmission was developed by Volkswagen for their Cabrio, Jetta, Golf, GTI, and New Beetle models built between 1995 and 2005, as well as Passats with transverse engines manufactured between 1995 and 1997. The 01M transmission is hydraulic / electronic 4-speed automatic transmission.
Electronically controlled with a lockup torque converter, the 01M transmission uses planetary gears, a gear-driven drive with an open-differential, and clutch packs. The 01M transmission is void of an internal chain and does not accommodate a dipstick as Volkswagen did not want vehicle owners to accidentally add inferior or incorrect transmission fluid to the unit.
The transmission oil in the 01M transmission is both heated and cooled by the engine antifreeze running through the cooler. Additionally the 01M transmission has an oil-to-liquid cooler which is located on the top of the unit.
Common areas of failure on the 01M transmission pertain to damage incurred to the plastic internals as a result of the transmission fluid over-heating, torn piston diaphragms resulting in internal pressure leaks, solenoids with worn piston bores in the aluminum valve body, as well as the resulting worn bands and clutches. Sometimes the speedometer drive gear (plastic) can be damaged and break off the differential carrier causing the speedometer to cease working. Repairing this requires that the transmission is removed from the vehicle and the differential taken apart enough to replace the internal plastic gear. Over time, the resistance located in the electrical terminals and wiring between the transmission and the valve body can increase. This increased resistance can prevent the computer from identifying the faint signals from the speed sensors in the 01M transmission. Thus when a signal is missing the result will cause the transmission to incur a "fail safe" mode. The fail safe mode will keep the unit in 3rd gear and the instrument panel indicator will indicate that all gears are selected at the same time.
When the 01M transmission requires replacement, special attention should be given to the specific transmission code (three characters that are stamped on a pad right above the flange for the starter). The 01M transmission was offered with several gear ratios for varying engines and vehicles, and as such it is critical to obtain replacement transmission with the identical code or another code that has identical gear ratios. If the gear ratios do not match, the transmission controller will determine that the transmission is slipping and result in the unit going into fail safe mode.
As the 01M transmission is a very specialized unit that was built only for vehicles manufactured by Volkswagen, most local transmission shops as well as national chains do not have specific knowledge, equipment, or training to test and re-machine the most important parts of the unit. As a result, multiple "teardowns" - under warranty - may be required for an acceptable outcome.
Synthetic mineral oils, such as Volkswagen G 052 162 A2 3 liters or Pentosin ATF-1 are the correct fluids for the 01M transmission are acceptable for a filter change. Checked from underneath, the fluid should be checked while the vehicle is running and in park. The fluid level should be inspected before the transmission has completely warmed up. A 5mm allen wrench is used to remove the drain plug that is located on the bottom of the transmission oil pan. Regardless of the level being low or full, one can expect some fluid to drip out. Similar to a chimney, the 01M has a plastic stack in the hole that prevents all the fluid from coming out. The stack ensures that the proper level is maintained at varying temperatures. When the fluid is just barely coming out of the bottom hole in temperature ranges between 95-113F, no additional action is needed and the drain plug can be installed and the tube cap filled.
The 01M requires separate fluid for the differential resulting in two fluid levels requiring checking. To inspect the fluid level for the differential, the speed sensor gear assembly is unscrewed and used as a dipstick. The assembly for the speed sensor is found on top of the transmission and right above the right inner CV joint. Emptying the differential involves removing the final drive cover (located on the rear of the transmission) or by vacuum extraction via the hole in the speed sensor. The optimal method is vacuum extraction due to the fact that a paper gasket seals the steel cover and access can be challenging. Filling is accomplished through the speed sensor hole. The capacity for the differential is about 1 liter of oil. It is very important to be cautious to not get sand or dust into the differential unit as the differential can not filter its fluid.
The 01M transmission's shifting is controlled by the TCM (Transmission Control Module). The TCM utilizes "fuzzy logic" that actually learns the driving tendencies of the operator to help determine what to do next. If and when multiple drivers, having varying driving styles, operate the vehicle, the result can be a confused TCM that starts becoming goofy. This goofy behavior may result in slipping, hard shifting, and challenges getting into gear at idle. When this happens, sometimes a quick fix correcting the fuzzy logic can be achieved by sitting in the driver's seat and turning the ignition on without starting the car. Then immediately putting the accelerator to the floor and counting to five. When done, take foot off the pedal, rotate the key to the off position, and immediately start the engine. If a confused TCM is the problem, this should solve the problem. It should be noted that this does not reset trouble codes in the computer which must be done with the proper OBDII scanning tool.
The computer for the 01M transmission can be found underneath the back seat of the Golf Mk3, Passat, and Jetta models. On the New Beetle models the computer is located underneath the right side dashboard cover. In other Volkswagen Jetta and Golf Mk4 models the computer is located in the wiper area plenum.
Production of the 01M transmission by Volkswagen ceased with the last of the Mk4 body style for Golf in the year 2006. The unit was succeeded by the 5-speed automatic 09A Tiptronic, and afterward by the 6-speed 09G Tiptronic automatic transmission, designed by Aisin, in New Beetle Convertibles. Additionally, the Direct-Shift Gearbox based dual clutch transmission in more current models of the previously mentioned models. The DSG (Direct-Shift Gearbox) is void of a torque converter and is more comparable to a two manual transmissions found in a single housing.
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